@rookieweeb seems like it means their hearts have stopped but they're still functioning as if they hadn't. Doctors say time of death is when the heart stops so technically they are "dead"
So even if they grind their bodies up they won’t actually die. They’ll be forced to revive through that painful process, it’s basically an immortality disease
Seems so far coherent. Not sure it'll be too interesting if all cases are like this one, but presumably that was just the introduction. Hopefully the totally-not-a-zombie thing isn't just there to have random gore all the time for no reason.